Deuteronomy 21:1-9

“If in the land that the LORD your God is giving you to possess someone is found slain, lying in the open country, and it is not known who killed him, then your elders and your judges shall come out, and they shall measure the distance to the surrounding cities. And the elders of the city that is nearest to the slain man shall take a heifer that has never been worked and that has not pulled in a yoke. And the elders of that city shall bring the heifer down to a valley with running water, which is neither plowed nor sown, and shall break the heifer’s neck there in the valley. Then the priests, the sons of Levi, shall come forward, for the LORD your God has chosen them to minister to him and to bless in the name of the LORD, and by their word every dispute and every assault shall be settled. And all the elders of that city nearest to the slain man shall wash their hands over the heifer whose neck was broken in the valley, and they shall testify, ‘Our hands did not shed this blood, nor did our eyes see it shed. Accept atonement, O LORD, for your people Israel, whom you have redeemed, and do not set the guilt of innocent blood in the midst of your people Israel, so that their blood guilt be atoned for.’ So you shall purge the guilt of innocent blood from your midst, when you do what is right in the sight of the LORD.